In droplet-based microfluidic devices, a liquid is sandwiched between two parallel plates and transported in the form of droplets. Droplet-based microfluidic systems offer many advantages: low power consumption and require no mechanical components such as pumps or valves. In recent years, droplet-based microfluidic systems have been broadly utilized in applications such as the mixing of analytes and reagents, the analysis of biomolecules, and particle manipulation. In digital microfluidic systems, electro-wetting-on-dielectric (EWOD) and liquid dielectrophoresis (LDEP) are the two main mechanisms that are used to dispense and manipulate droplets. EWOD and LDEP both exploit electromechanical forces to control the droplet. EWOD microsystems are usually utilized to create, transport, cut, and merge liquid droplets. In these systems, the droplet is sandwiched between two parallel plates and actuated under the wettability differences between the actuated and nonactuated electrodes. In LDEP microsystems, the liquids become polarizable and flow toward regions of stronger electric field intensity when a voltage is applied. The differences between LDEP and EWOD actuation mechanisms are the actuation voltage and the frequency. In EWOD actuation, a DC or low-frequency AC voltage, typically between 50 Vrms and 100 Vrms, is applied, whereas LDEP needs a higher actuation voltage (100-300 Vrms) and a higher frequency (50-200 kHz).
To manufacture the microfluidic system, conventionally it requires constructing high voltage electrodes to perform droplet actuation. Typically the top plate then is used as electrical voltage reference (or ground).